Variable displacement engines may employ a valve deactivation assembly including a rolling finger follower that is switchable from an activated mode to a deactivated mode. One method for activating and deactivating the rocking arm includes an oil-pressure actuated latch pin within the inner arm of the rolling finger follower. In a first mode, the pin engages the inner arm and outer arm in a latched condition to actuate motion of the outer arm, thereby moving a poppet valve that controls one of the intake or exhaust of gases in the combustion chamber. In a second mode, the inner arm is disengaged from the outer arm in an unlatched condition, and the motion of the inner arm is not translated to the poppet valve.
Mode transitions, either from the latched condition to the unlatched condition, or vice versa, may be designed to occur only when the cam is on the base circle portion. For example, mode transitions may be controlled to occur only when the roller follower is engaging the base circle portion of the cam. This ensures that the mode change occurs while the valve deactivator assembly, and more specifically the latching mechanism, is not under a load.
Due to the high rotational speed of a cam, it may be difficult to reduce the amount of time needed to transition from a latched condition to an unlatched condition in order to execute the transition during a single base circle period. The inventors have recognized that one problematic issue that may arise during mode transitions in a rolling finger follower with an oil-pressure actuated latch pin is the presence of air within the latch pin circuit, which is compressible and increases the amount of time needed to switch from the latched condition to the unlatched condition or vice versa.
The latch pin hydraulic circuit of a switching rolling finger follower may be primed with a low amount of hydraulic pressure while operating in the latched condition to facilitate the transition to the unlatched condition. In one example, this priming is achieved by utilizing a dual-function hydraulic lash adjuster (HLA) which is configured to provide hydraulic fluid to a latch pin hydraulic circuit at one of a first, lower pressure or a second, higher pressure. The first and second pressures are provided to the hydraulic lash adjuster via respective first and second ports, and the lash adjuster directs the hydraulic fluid to the latch pin hydraulic circuit via a single port. One example of such a hydraulic lash adjuster is shown by Smith et al. in U.S. 2014/0283776. The hydraulic lash adjuster may be included within a valve deactivation hydraulic circuit that provides a lower hydraulic pressure to the first HLA port via a first hydraulic gallery whenever the engine is running, and selectively provides a higher hydraulic pressure to the second HLA port via a second hydraulic gallery when an unlatched condition is desired. The higher hydraulic pressure is above a threshold pressure for switching the state of the latching mechanism within the latch pin hydraulic chamber. The lower hydraulic pressure may be supplied via a dedicated HLA supply, while the higher hydraulic pressure may be selectively supplied by energizing a dedicated variable displacement engine oil control valve (VDE OCV). The priming of the switching gallery may be achieved by routing at least a portion of the HLA hydraulic pressure through a hydraulic flow restrictor coupling the first and second hydraulic galleries. In this way, an amount of hydraulic pressure, less than the threshold switching pressure, is present within the second hydraulic gallery when the VDE OCV is de-energized, allowing for a quicker transition to an unlatched condition upon energizing the VDE OCV.
However, the inventors herein have also recognized potential issues with such systems, particularly with regard to the issue of air entrapment in the oil. As one example, pockets of air may be introduced to the higher pressure hydraulic gallery when the engine is not running. Upon energizing the VDE OCV for valve deactivation, this air may be directed to the HLA and/or the latch pin hydraulic circuit along with the high pressure hydraulic fluid. This entrapped air can interfere with oil compression within the latch pin hydraulic circuit, thereby increasing the mode transition time in an unpredictable manner. The resulting longer and/or unpredictable mode transition times are undesirable.
In one example, the issues described above may be addressed by a method for an engine valve deactivation mechanism, comprising supplying a first oil pressure to each of a switch of a rocker arm and a pressure relief valve via a priming gallery and a hydraulic lash adjuster oil gallery; and selectively supplying a second oil pressure, greater than the first oil pressure, to the switch of the rocker arm via the hydraulic lash adjuster oil gallery. In this way, if the priming gallery is coupled to the hydraulic lash adjuster oil gallery, air entrapped within the hydraulic lash adjuster oil gallery may be expelled from the valve deactivation hydraulic circuit via the priming gallery and the pressure relief valve, thereby reducing mode transition times and increasing the predictability of the mode transition times.
As one example, the dedicated priming gallery may run parallel to the switching gallery, and may be coupled to the high pressure HLA gallery via a perpendicular drilling located toward a rear end of a cylinder head. By positioning the drilling immediately upstream of the couplings between the high pressure HLA gallery and the hydraulic lash adjusters, air may be diverted from the high pressure gallery before reaching the hydraulic lash adjusters, thereby improving the response times for valve deactivation. The dedicated priming gallery may receive a small hydraulic pressure from a dedicated hydraulic flow restrictor incorporated into the distal end of a VCT OCV valve body. By incorporating the restrictor into an annular clearance defined by an outer diameter of the valve body and an inner diameter of a mating bore of the valve body, which are both machined with tight tolerances, a controlled amount of pressure may be supplied to the priming gallery. In this way, the high pressure HLA gallery may be reliably purged of air.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.